A related invasive mussel, the quagga mussel, has less pronounced stripes, which tend to fade near the hinge. Both the zebra and quagga mussels are native to inland lakes in Russia.

Spiny Waterflea

Competes with native fish for food. Fouls fishing gear. Difficult to distinguish individuals without magnification. 1/4″ to 5/8″ total length. One to 4 pairs of barbs on tail. Prominent, tiny, dark eyespot. Clumps look and feel like gelatin. Females produce eggs that resist drying, so they may survive on boats and trailers between lakes.

First confirmed in Big Bay in 2015. Monitoring spread. May be present in other bays. Please report any new infestations.

Eurasian Watermilfoil

Found in waters up to 20 feet deep. May form dense mats in waters up to 15 feet deep. Interferes with fishing, boating and swimming. Three to five feathery leaves arranged in whorls (circles) on stems. Each leaf has 12-21 leaflet pairs. A native look-alike — northern watermilfoil — has only 5-10 leaflet pairs.

Curly-Leaf Pondweed

Forms weed mats that shade out native plants. Grows from the shore to depths up to 15 feet. Leaves somewhat stiff and crinkled, 1/2 inch wide, up to 2-3 inches long, arranged alternately around stem. Has small “teeth” visible along edge of leaf.

Small, isolated infestations in Everett and Stuntz Bays. Treating and monitoring for spread. Please report any new infestations.

Rusty Crawfish

Can harm sport fish. Grazes on and eliminates aquatic plants. Displaces and can hybridize with native crayfish. Adult 3-5 inches long. Claws larger and smoother than other crayfish. Carapace marked with a pair of dark, rust-colored spots.

Significant infestations in the east basin, except soft-bottom bays. First noted in 1980s. Slow expansion westward.

Purple Loosestrife

A hardy perennial which can rapidly choke wetlands. Height 3-7 feet. Spikes covered with many flowers. Flower has several pink-purple petals. Downy smooth-edged leaves. Leaves usually paired opposite. Mature plants have many stems that grow from a root crown. Dead stems stand until spring.

Occasional, isolated infestations along shorelines or adjacent wetlands. Treating and monitoring for recurrence. Please report any new infestations.